B. Shipping Fever

Shipping fever occurs in all parts of the world. It may affect cattle of any age or type. A few or most of the animals in a herd may be affected. It is particularly prevalent in feeder cattle just after they have been moved from the range or from their home environment to the feed lot.

It may occur in any season, but most cases are in fall, when most of the movement occurs. The crowded feeder cattle traffic lanes apparently become quite contaminated, thus increasing the exposure of the animals to all infections. Stockyards, sales barns and other yards, railroad cars, trucks and other vehicles, and private feeder yards become contaminated. It is possible that healthy-looking or recovered animals may carry and spread the infection.

Stress conditions are major predisposing factors for shipping fever, especially the excitement, exhaustion, and changes of feed and water that attend the shipping of animals. Irritation of the respiratory mucous membrane by dust stirred up during movement, overcrowding, long periods without feed and water, and weather changes also frequently are predisposing factors.

Calves weaned just before being shipped seem to be most susceptible, probably because they are more excitable and because they experience more marked feed changes than older cattle. Resistance increases with the age of the animals.

Good physical condition seems to afford little protection against incurring shipping fever, but it undoubtedly is a factor in avoiding complications and serious losses. Poorly nourished and highly parasitized animals usually are more seriously affected and less responsive to treatment. Deficiencies, particularly of vitamin A, could also be expected to reduce the resistance of the animals against respiratory infection.